This invention relates to a dental filling material capable of forming a cured product or filling with improved mechanical properties.
Recently, for the treatment of dental caries, composite resin has been often used as a dental filling material because it has many advantages of easy application, safety and matching color as compared with conventional filling materials such as amalgam, inlay and cement. A composite resin generally comprises monomers, polymers, inorganic fillers, catalysts or curing agents, colorants, stabilizers and the like. The composite resin usually consists of a two-paste system, one paste containing an amine catalyst, and the other paste containing a peroxide catalyst. The two pastes are formulated so as to be cured within about five minutes when a dentist mixes them. An ultraviolet-curable system is also available.
In these types of dental filling materials or composite resins, physical properties are important, including hardness, flexural strength, compressive strength, abrasion resistance, water absorption and the like. A number of filling materials have been formulated with special attention paid to physical properties, as disclosed in Bowen, U.S. Pat. No. 3,066,112, Switzerland Pat. No. 557,674, and Japanese Patent Application Laid-Open No. 48-45092. These filling materials are, however, not necessarily satisfactory in strength as compared with metallic materials. There has been a need for a dental filling material capable of forming a cured product having enhanced strength and improved physical properties.
The inventors have found that by using a monomeric reaction product of two moles of a hydroxyalkyl diacrylate or dimethacrylate with one mole of an organic diisocyanate (to be referred to as "diurethane tetraacrylate or tetramethacrylate", hereinafter) as a polymerizable monomer of a dental filling material, there is obtained a dental filling material capable of forming a cured product which not only has improved properties required for dental fillings, particularly, improved hardness, compressive strength, flexural strength and tensile strength, but also has a color tone quite similar to the tooth enamel such that substantially no aesthetic difference may be perceptible between the cured filling and the adjoining tooth enamel. This filling material is useful for actual dental treatment.
It has been known from G. B. Pat. No. 1,401,805 and G. B. Pat. No. 1,430,303 that formulating urethane diacrylate results in a cured product which is water white in color and aesthetically acceptable. However, the use of diurethane tetraacrylate or tetramethacrylate to form a cured product with improved physical properties is novel as far as the inventors know.